Early this morning, commenting on last night’s returns, Hugh Hewitt, “writing,” in his own words, “the same thing” he’s been saying “since late January: The race for the GOP nomination is still over. It has been over since Florida.” Was, as Hugh claims, Mitt Romney’s victory in Florida was the decisive moment in the current contest for the Republican presidential nomination?

Much as I respect Hugh, I believe otherwise. In the wake of his February hat trick, winning Colorado, Minnesota and Missouri all on the same day, Rick Santorum had a read chance to capture the Republican nomination. Polls showed him ahead in such upcoming contests as Michigan and Washington State. Romney’s margin in Arizona was slipping down into the margin of error. He surged ahead in the Gallup tracking poll.

With his relentless campaign, facilitated by his campaign’s deep pockets, Romney fought back, whittling Santorum’s lead, stanching his rival’s surge. Even as polls started moving his way (a bit), he still lagged behind.

Was the decisivie perhaps the Mesa debate just six days before the Arizona and Michigan primaries where the former Massachusetts governor outperformed his rival from the Keystone State? Or did it come later when Romney won the Michigan primary by 3 points (even as Democrats voted in the Republican primary to help his opponent)? Or was it the Ohio primary which he won narrowly?

Or perhaps that moment came just two weeks ago when Romney won Illinois so decisively? Or was it his own hat trick last night?

Another relatively useful metric is the date on which a candidate secured a lead in national polls that he never relinquished. This method provides a fairly intuitive answer when applied to past elections — for instance, it would suggest that John Kerry won the Democratic nomination in 2004 after Iowa, after which he never really looked back, or that Michael Dukakis won the 1988 Democratic nomination shortly after Super Tuesday.

Michigan — actually, a few days before Michigan — again emerges as the key turning point by this measure. Mr. Romney has led his rivals in the Gallup national tracking poll every day since Feb. 25.

That Feb. 25 date stands out for another reason: it was the first time in the tracking poll that the majority of Gallup’s interviews were inclusive of the Feb. 22 Republican debate in Arizona. The final margin in Michigan was close enough — just three percentage points in Mr. Romney’s favor — to suggest that the debate may have swung the difference.